Matthews allegedly told police he carried out the kidnapping to teach his stepsister a lesson because he believed she was “selfish” and treated his mother badly, prosecutors said during the couple’s trial in Bristol on Wednesday.

Parts of Watts’ body were found in a shed encased in layers of plastic and salt less than two weeks after she went missing, The Guardian wrote. Her body had been dismembered with a circular saw and a post mortem examination found that the girl had been stabbed 15 times in the abdomen after she died and had been struck in the neck with a screwdriver, prosecutors told a horrified courtroom.

Matthews, who allegedly wore a mask and brought a stun gun and handcuffs to carry out his plot, said his face cover slipped as he struggled with Watts in her bedroom and so he strangled her, The Guardian wrote.

But prosecutors insisted that the couple had extensively plotted to kidnap Watts for sexual reasons and that both concealed their victim’s body.

Messages exchanged between Matthews and Hoare showed they shared an interest in teenage girls and discussed kidnapping one, The Guardian reported.

Video footage was played for the jury showing the couple shopping for bleach, trash bags, rubber gloves and plastic wrap that was allegedly used to hide the body and clean the bathroom where the dismembering supposedly took place.

Evidence presented to the jury also claimed that the couple left their home at 10:50 a.m. on the day Watts disappeared and stopped at a supermarket for batteries, which were “possibly for a stun gun,” Prosecutor William Mousley said in court Wednesday.

Surveillance footage from that day also showed the couple driving with a child in the backseat of their car.

The couple was arrested for kidnapping on February 28 and two days later, when Watts’ body was found, they were charged with murder. Cops said they recovered two allegedly illegally-owned stun guns during a raid of their shared home, the paper reported.

Video from a hardware shop showed Matthews buying a power saw, gloves, goggles and a face mask a day after Watts went missing and prosecutors said the couple used the items for the dismemberment, The Guardian reported.

Prosecutors alleged the couple dismembered and packaged Watts’ body over the course of two days, eventually moving the body parts to a shed near their home with the help of four people.

The owners of the property where the shed stood on admitted they agreed to help hide packages, but they claimed they thought they were hiding a bag of marijuana, The Guardian wrote.

Police discovered Watts’ body parts inside suitcases and other containers in the shed. The girl’s family members sobbed as the gruesome details were recalled and one loved one needed to leave the courtroom, the paper reported.

Hoare pleaded not guilty to kidnapping, murder, preventing burial, preventing the course of justice and possessing illegal stun guns, The New York Daily News wrote. The paper also noted Matthews pleaded not guilty to the murder and kidnapping charges, but admitted to preventing lawful burial, preventing the course of justice and possessing the stun guns.